The present invention relates generally to electro-optical displays, and more particularly to forming modulated signals that digitally drive display elements.
Typically, a display system includes a display device that receives drive control information for driving display elements, displaying desired content. More specifically, for digitally driving a display device a commonly shared drive control data may be sent to each display element as a reference signal in addition to appropriate per-pixel display data (e.g., a pixel value). For example, an array of display elements (e.g., pixels) in a display device may be driven using drive signals, such as modulated waveforms that may be formed based on the common drive control data and per-pixel display data. In doing so, each modulated waveform may be individually formed to drive a different pixel of the display device. However, there are many ways to generate these drive signals.
One approach to form drive signals in display systems involves using pulse width modulation (PWM). By generating pulse width modulated waveforms, pixels with available digital storage, such as in liquid crystal displays (LCDs) may be appropriately driven. In one pixel architecture, per-pixel circuitry may modulate the orientation of liquid crystal (LC) material of a pixel.
To generate a modulating signal, such as a PWM waveform, a refresh period (or modulation cycle) may be divided into “m” discrete steps. For these steps, a counter may keep a step count as a counter value. At each step, the per-pixel circuitry may elect to change the state of the pixel based on the step count and pixel value of the pixel. Typically, the per-pixel circuitry makes the state transition decision by mapping a counter value from an interval counter (e.g., an m-bit counter) into an n-bit space (where “n” is the number of bits in the per-pixel display data). For example, by asserting that the state of the PWM waveform for a pixel of value “p” is 0 if “p” is less-than the mapping of the current counter value of the interval counter onto the n-bit space, a programmable storage device, such as a look-up-table (LUT) may enable this n-bit space mapping.
Using the m-bit counter output onto a different set of numbers, i.e., a 2m×n LUT, a n-bit ramp value for use at each pixel may be provided to accomplish this mapping in one case. The n-bit value, however, should be monotonically increasing. Moreover, the fidelity with which a given non-linear relationship may be represented depends on the value of “m”. Therefore, typically a large value is desired for “m,” requiring a look-up-table (LUT) of a relatively much larger size than necessary to support a ramp-based technique. Even worse, programming such a large look-up-table (LUT) may be inefficient, especially when most of the entries in the LUT do not change. As a result, a large LUT may waste precious hardware real estate in some displays.
Thus, there is a continuing need for better ways to form modulated signals that drive display elements with available digital storage.